Upgrade to Camel 4.0.0

This commit upgrades Spring Boot 3.x to use Camel 4.0.0. It also
documents the version to use for Spring Boot 2.6.x

See gh-1280

start-site/src/main/resources/application.yml

@@ -835,11 +835,11 @@ initializr:
           compatibilityRange: "[2.6.0,3.2.0-M1)"
           mappings:
             - compatibilityRange: "[2.6.0,2.7.0-M1)"
-              version: 3.17.0
+              version: 3.14.9
             - compatibilityRange: "[2.7.0.M1,3.0.0-M1)"
               version: 3.20.6
             - compatibilityRange: "[3.0.0-M1,3.2.0-M1)"
-              version: 4.0.0-RC2
+              version: 4.0.0
           description: Apache Camel is an open source integration framework that empowers you to quickly and easily integrate various systems consuming or producing data.
           groupId: org.apache.camel.springboot
           artifactId: camel-spring-boot-starter